As well as having a tailored functionality, modern plastics are also intended to do increased justice to environmental concerns. As well as by a general optimization of preparation processes, this can also be achieved through the use of greenhouse gases, such as carbon dioxide, as building blocks for the synthesis of polymers. Accordingly, for example, a better environmental balance for the process can be obtained overall via the fixing of carbon dioxide. This path is being followed in the area of the production of polyethercarbonates, and has been a topic of intense research for more than 40 years (e.g., Inoue et al, Copolymerization of Carbon Dioxide and Alkylenoxide with Organometallic Compounds; Die Makromolekulare Chemie 130, 210-220, 1969). In one possible preparation variant, polyethercarbonate polyols are obtained by a catalytic reaction of alkylene oxides and carbon dioxide in the presence of H-functional starter compounds (“starters”). A general reaction equation for this is given in scheme (I):

A further product, in this case an unwanted byproduct, arising alongside the polyethercarbonate polyol is a cyclic carbonate (for example, for R═CH3, propylene carbonate).
The literature describes a number of different preparation variants. For example, US 20100048935 A1 describes a process for the preparation of polyethercarbonate polyols by reaction of alkylene oxides and carbon dioxide with H-functional starter compounds by means of a DMC catalyst, wherein one or more starter compounds are initially introduced in a reactor and additionally one or more starter compounds are metered in continuously in the course of the reaction. Epoxidized soyabean oil is mentioned as a possible alkylene oxide. The reactivity of these oxirane rings, however, is low, since they are inside a chain and are greatly sterically shielded. Accordingly, the epoxidized soyabean oil is reacted more slowly than customary monomers, such as propylene oxide, and accumulates in the reaction mixture. Since, moreover, epoxidized soyabean oil constitutes a mixture of multiply epoxidized compounds, the controlled construction of defined polymer architectures is not possible.
WO 2006/103213 A1, in contrast, describes a process for the preparation of polyethercarbonate polyols with improved incorporation of CO2 into the polyethercarbonate polyol, using a catalyst featuring a multimetal cyanide. The specification discloses the presence of an H-functional starter, an alkylene oxide, and carbon dioxide in the presence of the multimetal cyanide component in a reactor. The document further discloses the presence of a CO2-philic substance or of CO2-philic substituents. The CO2-philic substance or the CO2-philic substituent is said to facilitate the incorporation of the CO2 into the polyethercarbonate polyol and thereby to reduce the formation of cyclic alkylene carbonates, such as propylene carbonate, for example, which represent unwanted byproducts.
WO 2012/033375 A2 discloses a process for the preparation of crosslinked polycarbonate polyols by alternating addition of carbon dioxide and alkylene oxides onto H-functional starter compounds in the presence of a catalyst.
U.S. Pat. No. 3,699,079 A discloses a process for the preparation of copolymers from carbon dioxide and diepoxides in the presence of a catalyst system.
Furthermore, however, it may be desirable also to obtain polyethercarbonate polyols of relatively high functionality which have a viscosity suitable for further processing and have a relatively high number of reactive, terminal groups. These polymers may advantageously also be of branched construction and in further crosslinking reactions may lead to crosslinked polyethercarbonate polymers which feature improved molding or film qualities.
In principle it is also possible to obtain polyethercarbonate polyols of relatively high functionality by using oligomeric multifunctional starter molecules, usually with functional OH groups. The viscosity of the products obtained in such a way, however, is frequently heightened. Furthermore, such starters must often be synthesized in a separate step. The synthesis of the starters usually entails using bases as catalyst. Before these starters are used in a catalysis with DMC catalysts, they must be purified, at cost and inconvenience, to remove basic catalyst residues. The use of low molecular mass multifunctional starter molecules results in a reduced activity or even in complete inhibition of the DMC catalyst. It is therefore necessary to use high concentrations of catalyst or to accept long reaction times. For a given OH number, polyethercarbonate polyols prepared with multifunctional starter molecules have a viscosity which increases in line with the functionality. Accordingly, EP 12181907.2-1301, for a polyethercarbonate obtained using glycerol as trifunctional starter, describes a significantly increased viscosity (36.0 Pa·s) in comparison with a polyethercarbonate obtained using dipropylene glycol as difunctional starter (4.1 Pa·s).